1. Field of the Invention
The present invention generally relates to impact breaking and crushing of rock and, more particularly, is concerned with a improved centrifugal impactor for crushing rocks. The term "rocks" as used herein is meant to include a wide variety of solid materials.
2. Description of the Prior Art
Centrifugal impactors, such as disclosed in U.S. Pat. Nos. 3,970,257 and 4,662,571 to MacDonald et al, have provided the rock crushing industry with mechanisms for producing small rock particles. The mode of operation of these centrifugal impactors is as follows. Incoming rocks are fed into a rotor from above through a feed eye ring, near a vertical rotational axis of the rotor. The incoming rocks are engaged and impelled outwardly under centrifugal force by a plurality of circumferentially arranged and spaced vanes of the rotating rotor. A vane tip is located at the radially most distant point on each vane along the path of a rock's movement in the rotor relative to the vane. Rocks moving in the rotor exit past the tips of the vanes through discharge openings between the vanes and are then broken either by impact with other rocks or upon impact with some part of the centrifugal impactor itself appropriately positioned radially outwardly from the rotor.
On the rotor, the feed eye ring is comprised of a wear resistant replaceable part which protects the rotor entry opening from excess abrasion. The tips of the vanes are readily abraded by the stream of impelled rocks being discharged past the vane tips. In the past, attempts to reduce tip wear have relied primarily upon capturing a layer of rock in the vanes on the rotor to reduce the wear to the vanes and also in making the extremity of each vane tip, called a "tip carrier", of wear resistant material.
Examples of tip carriers using a fixed wear-resistant material are disclosed in U.S. Pat. No. 3,346,203 to Danyluke and U.S. Pat. No. 4,940,188 to Rodriguez et al. In these devices, a layer of rock builds up in front of the vane and inside the tip to protect most of the vane from continual wear. Rocks leaving the vane still have to pass around the tip carrier which is fixedly connected to the vane. The relative velocity and angle of trajectory between the moving rocks and the tip carrier fixed to the vane largely determines the degree of abrading action taking place at the tip carrier. The wear-resistant material used in the tip carriers is brittle and can be broken and destroyed by impact with the centrifugally moving rock.
Many conventional rotors also have outer wear-bits to protect the sides of the rotor housing. These wear-bits are located outside and behind the tip and are positioned to deflect rocks that are rebounding in such a way as to strike the outer wall of the vane. These bits are regularly broken by the impact force of rebounding rock.
To further protect the rotor by reducing the size of the rocks being fed into the rotor, separating and by-passing devices have also been developed. An example is the screen disclosed in the aforementioned U.S. Pat. No. 4,662,571 to MacDonald et al being formed by a conically-arranged series of concentric rings. The problems with a cone type screen of the MacDonald et al patent are the increasing radius which varies opening size, the resultant low screening area, and the increase in overall height of the machine added by this type of screen.
A different centrifugal impactor disclosed in U.S. Pat. No. 3,834,631 to King employs a symmetrical bowl-shaped rotor without any a feed eye ring nor a plurality of vanes with vane tips. The principle of operation of this centrifugal impactor is as follows. Rocks are fed from above into the rotating bowl-shaped rotor. Some rocks are thrown against the interior surface of the bowl sidewall and held in place by centrifugal force. As more rocks are fed into the bowl-shaped rotor the rock lining is supposed to build up to an equilibrium shape in the form of a paraboloid-like surface with its open end toward the upper open end of the rotating bowl-shaped rotor. Thereafter rocks are discharged from the rotor as fast as they enter.
Since there are no vanes in the rotor of this centrifugal impactor, the rocks are acted upon and caused to rotate or spin on their own axes as they are discharged from the rotor largely due to the force of friction produced by contact with the rotating rotor and the rock lining therein which rotates with the rotor. The net effect of the spinning action of the rocks and their impact with the lining of rocks in a trap chamber of the impactor which surrounds the rotor is that they break apart into smaller fragments.
However, a major problem with the rotor of the King centrifugal impactor is vibration due to unequal loading of the rotor sidewall. In most instances, the lining of bowl-shaped rotor with rocks will not be symmetrical. Oftentimes, a larger piece of rock will lodge against the interior of the rotor sidewall and act as a dam, holding even more rocks. The lining of the rotor will then become two or three inches thicker on one side than the other. In time, new entering rocks will grind this condition away, only to have it reoccur. The persist occurrence of a non-symmetrical lining will throw the rotor out of balance, requiring shutdown of the machine due to excessive vibration.
From the above description of the various problems associated with prior art centrifugal impactors, it can be seen that need exists for improvements to alleviate these problems without introducing new ones in their place.